When a unit is reduced to 0 health mid-chain (via Stupefy countering Cleave after Ray of Siphoning was played), does the unit die before the countered spell resolves?

Ruling: Kai'Sa dies during the cleanup after Stupefy resolves, before Cleave has the chance to resolve.

Sequence:

• Opponent moves red Kai'Sa into Watchful Sentry
• Opponent passes focus
• You play Ray (of Siphoning), focus passes
• Opponent plays Cleave
• You chain Stupefy (countering Cleave)
• Stupefy resolves
• Cleanup occurs - Kai'Sa dies
• Cleave does not resolve (it was countered)